1. Field of the Invention
The present invention is directed to an aperture detecting device for determining the two-dimensional address or location of a small aperture surrounded by regions, i.e., a background, of different optical brightness present on a plane surface such as the pattern film of a printed board.
Perforation of printed circuit boards and the like have hitherto been effected automatically by means of an NC machine. If the perforation is performed after reading an arbitrary pattern, however, there exists no device for automatically determining the two-dimensional location or site of a hole on the board.
2. Description of Prior Art
Recognizing this need, the applicant of the present invention previously developed the device disclosed in Japanese Patent Application No. 63-201055. This prior arrangement forms the basic context of the present invention and thus appears in FIGS. 1 and 2 of the present drawings to which reference may be had for the following description. The prior device comprises: an optical image sensor for outputting electrical image signals varying according to image brightness in the form of pulses P having a binary value, i.e., one logic state, e.g. 1, for the background region, and another logic state, e.g. zero, for the aperture regions, by effecting linear scanning at a given rate of a plane surface 1 while sequentially shifting in steps of a fixed distance the linear position of sensor 2 in an orthogonal direction relative to the scanning direction; a pulse generating means 3a receiving pulses P, and generating therefrom pulses P.sub.2 each having a duration or length set or fixed to correspond to a scanning time or pulse duration slightly greater than a diameter of the apertures to be scanned; a logical product means 3 receiving the set pulses P.sub.2 and emitting a signal (logic 1) when the product of the input signals is logic 1, i.e., both are at logic 1 as the image signal pulses P.sub.3 ; time-delay means 4 for delaying signal pulse P.sub.3 for a time sufficient to permit a synchronous comparison of the output signal pulses given by the logical product means 3 for at least the newest (last) and oldest (first) scan lines among a group of successive scan lines equal to N+1 where N is the number of scan lines necessary to cover or spanning the orthogonal dimension of the apertures; a small-hole judging means 5 for outputting an aperture detecting signal, indicative of the presence of the aperture, when a logical product pulse P.sub.3 is absent from the output signals for the latest non-time delayed scan line l.sub.0 and for the oldest time-delayed scan line l.sub.N which are separated by at least one consecutive scan line l.sub.1 - l.sub.N-1 for which a logical product output pulse P.sub.3 is present, the judging means being inputted with the non-time delayed output signal from the logical product means 3 for line l.sub.0 and N-number of consecutive time-delayed output signals from the logical product means via time-delay means 4 for scan line l.sub.1 -l.sub.N, i.e., the output signals for a total of (N+1) number of consecutive scan lines, where a logical product output pulse P.sub.3 is present in the signal for at least one intervening scan line, e.g., l.sub.1, if N=2 or a plurality of consecutive scan lines including the latest line l.sub.1 which includes a time-delayed signal, e.g., lines l.sub.1 -l.sub.N-1, if N is more than 2; and an aperture address signal generating means 6 for outputting an aperture address signal with two dimensions or coordinates corresponding to the detection timing in the two dimensions or coordinates of the aperture detecting signal. That is to say, having identified the existence of an aperture by the detection of at least one consecutive line having a pulse P.sub.3 preceded and followed by a line having no pulse P.sub.3, the location of the aperture can be determined by the time along the line from a known starting point for the scan until P.sub.3 occurs and by the number of scan lines of a known separation or "pitch" from a known starting point until a line, or group of lines, having a pulse P.sub.3 occurs.
If the aperture address signal is to be used repeatedly, it is necessary that a storage means or memory 7 be connected to the aperture address signal generating means 6.
With this arrangement, the image sensor 2 effects a linear read-scanning process on the plane surface 1, and sequentially shifts the linear scanning position thereof in steps of a given pitch in the orthogonal direction. Consequently, as illustrated in FIG. 2, a binary-value real-time image signal pulse P.sub.1 is first generated when the scanning line crosses or intersects an encircling region 8a around the aperture 8. The image pulse P.sub.1 is inputted to the logical product means 3 together the set pulse P.sub.2 generated at the moment the scan line crosses the boundary between the region 8a and aperture, i.e., the leading peripheral portion of the aperture 8, due to the change in brightness between these regions during the linear scanning, and immediately the logical product means 3 outputs a logical product pulse P.sub.3. Since the set pulse P.sub.2 is longer than the maximum dimension of the aperture parallel to the scanning direction, the time-delay means 4 are intended to delay the output signals derived by the logical product means 3 for N number of inputted scan lines for a time sufficient to attain a synchronous comparison thereof relative to each other and the real time, i.e., non-delayed, optical signal from the latest (last) scan line.
Following this, the aperture judging means 5 outputs an aperture detecting signal after it judges the presence of an aperture when there is no logical product pulse P.sub.3 present in the real time output signals for scan line l.sub.0 which is the latest (last) in time among the (N+1) number of scan lines (all the scan lines to be judged at one time) and for the oldest (first) scan line l.sub.N among the delayed ones, provided a logical product pulse P.sub.3 is detected in one delayed output signal (e.g., for line l.sub.1 in FIG. 2 or in the delayed signals from each of plurality of consecutive lines l.sub.1 -l.sub.6 in FIG. 7 where N=7 and six is the maximum number of consecutive lines needed to span the orthogonal dimension, e.g., diameter, of the aperture within range of a timeframe Tr equivalent to a radius).
The aperture address signal generating means 6 serves to output an aperture address signal in two dimensions each time the aperture detecting signal is applied thereto.
The above-mentioned device is capable of automatically determining the two-dimensional address of an aperture for automatic machining thereof. When the position of a scan line coincides exactly with the periphery of the aperture, i.e., passes tangentially thereto, however, a plurality of aperture detecting signals may in some cases be generated for a single aperture on the occasion of a pulse waveform being disturbed at a first or last transition of the pulse waveform corresponding to the aperture. Thus, there is room for improving the operational reliability of this system.